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NENA Recommendation for the implementation of Inter-Networking,
E9-1-1 Tandem to Tandem

Document Type:

Standard

Number:

03-003 v1

This
NENA Technical Reference defines the use of an Integrated Services
Digital Network (ISDN) User Part (ISUP) signaling protocol between
E9-1-1 selective routing tandems, and similar equipment, for the purpose
of allowing 9-1-1 calls to be transferred or routed across E9-1-1
networks.

This Technical Reference is a guide for designers and
manufacturers of selective routing tandems and similar equipment. It may
also be of value to purchasers, maintainers and users of such
equipment.

This document describes the use of an ISUP Signaling to
allow appropriate information to be passed between E911 Tandem Network
Elements. An E911 Tandem Network Element is the switching element within
the telephone company network which receives 9-1-1 calls originated
within the Public Telephone Network, routes the call to the appropriate
Public Safety Answering Point (PSAP), and provides the signaling interface to the PSAP itself.

The purpose of utilizing ISUP Signaling is to facilitate
the delivery of all of the information necessary for an E911 Tandem to
provide the functions described above. That is, when an E911 Tandem
decides that a 9-1-1 call should be routed to another E9-1-1 Tandem, all
of the information necessary for the routing and delivery of that 9-1-1
call at another E9-1-1 Tandem should be passed in ISUP parameters in an
outgoing message to the second E9-1-1 Tandem. The information necessary
for properly routing and delivering a 9-1-1 call in this context is:

Calling Party Directory Number information Called Party Directory Number information (typically the digits "9-1-1”, but may have other values as described below)

Location Information (e.g. for wireless 9-1-1 calls,
location information must be passed for correct routing decisions to be
made)

Emergency Call Indicators (depending on the context
of the call, it may be necessary to use an indicator in the call to mark
it as a 9-1-1 call).

This technical reference will allow for two types of
interfaces between E9-1-1 Tandems. First, a dedicated, direct ISUP trunk
interface may be used between E9-1-1 Tandems. On this type of trunk
interface, all calls processed on the trunks are assumed to be 9-1-1
calls. As an alternative, this reference will prescribe the necessary
signaling for non-dedicated, non-direct trunks to be used for processing
9-1-1 calls. On these types of trunks, it cannot be assumed that calls
originating or terminating on the trunks are 9-1-1 calls.